What is dredging?
Dredging is the excavation of sediments and disposing of them at a different location. Material is dug or gathered from the bottoms of rivers, lakes, harbours and the open sea via number of methods, such as a giant scoop or high-pressure suction.
Various Australian waters have been dredged in the past, most notably Port Phillip Bay, overlooked by Melbourne, and, more recently, locations off the Queensland coast such as Gladstone harbour.
Why is it required?
Dredging is mainly used to either maintain the depth of ports or create new shipping channels. Large vessels require water of a certain depth to access these routes, so dredging is used to ensure they don’t run aground.
Sometimes the sediment from dredging is used to “renourish” onshore areas, such as coastal areas subject to erosion. The debris collected is usually a mixture of sand, mud and rock.
In the case of Abbot Point, dredging will be used to expand what is essentially a simple jetty jutting out into the sea into one of the world’s largest coal ports.
Greg Hunt, the environment minister, has approved dredging for three new port terminals, to be operated by a selection of Indian and Australian mining companies.
A total of 3m cubic metres of seabed will be removed to allow vessels to access Abbot Point, with up to 300m tonnes of coal shipped annually by 2020. The coal, extracted from the Galilee Basin in central Queensland, will be sold to overseas markets such as China and India.
Why is it controversial?
Marine environments are complex things. Removing large parts of the seabed and dumping it elsewhere can have a major impact on the ecosystem, particularly sensitive areas such as coral reefs and fish nurseries. Sediment can smother seagrasses, which are the key food source of dugongs and sea turtles, and damage corals.
The federal government requires dredging companies to obtain a permit to dump sediment, stating that fragile areas need “a high level of protection and/or management”.
Despite the regulatory framework around dredging, environmentalists claim oversight has been lax, causing damage to marine creatures. Some activists want dredging to be banned completely, blaming it for releasing toxic chemicals, increasing water turbidity and littering harmful metals throughout the food chain.
The tone of this debate has sharpened markedly since mining companies’ recent attempts to open up the Queensland coast to coal exports.
Dredging at Gladstone harbour has been extremely controversial, with critics claiming that a rushed, botched process saw sediment spill across the ecosystem, causing fish and crabs to develop lesions and die.
Conservationists and recreational fishers have blamed dredging for killing fish at Gladstone, although a government report blamed floods, rather than dredging, for washing harmful nutrients into the area.
The argument has now relocated to Abbot Point near the town of Bowen. The Greens have called Hunt’s dredging approval “criminal”, while others fret that an increase in shipping will cause damage to the Great Barrier Reef itself, hurting the $6bn tourism industry that relies on the World heritage-listed site.
However, business and local council leaders have welcomed the expansion of Abbot Point, which they see as vital in creating jobs in a region that has stagnated economically.
What does the science say?
The department of environment assessment of the Abbot Point project states that there is “no substantial risk” to the reef from increased shipping and concluded that dredged sediment is suitable for dumping in the Great Barrier Reef marine park.
North Queensland Bulk Ports, which is overseeing the project, said it has conducted a “rigorous and robust” assessment of the risks, pointing out that its modelling shows no adverse impact to corals or fish.
NQBP claims the science is on its side and that there is no unequivocal evidence that dredging, when conducted properly, is harmful to marine environments.
In August, the previous Labor government released a report it commissioned stating that spoil from dredging travels a lot further than previously thought, with dumped sediment capable of being disturbed repeatedly by severe weather. However, the analysis doesn't rule out dumping dredged waste at sea and suggests various locations near existing ports that would do the least damage to coral and other marine wildlife.
The report was seized upon by environmentalists but the Great Barrier Marine Park Authority, which oversees the health of the reef, recently clarified the findings, pointing out that time constraints meant the report was simplified and shouldn’t be an indicator of absolute risk.
However, recent research by James Cook University found it was likely that dredge spoil is more harmful to marine ecosystems than sediment washed into the sea by rivers.
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